Method of forming turbine rotors



.my 17, 1951Y w. N, MART|N` .mL 2,560,973

METHOD OF' FORMING TURBINE ROTORS Filed Dec. 5, 1945 4 Sheets-Sheet l millier zfwzm. :mlajzn/ Klzlde.

N. MARTINf-EtAL ME D oF FORMING TURBINE R July' 17, 1951 Filed Dec. 5, 1945 @M AWA/ Filed D 5; 1945 w. N. MARTIN rrr-A1.- 2,560,973 METHOD oF FORMING TURBINE RoToRsv July 17, 19511. w..N.-MART|N` Erm. 2,560,973`

METHOD OFVFORMING TURBINE-Ro'i'Rs v sneexs-she't .4

Patented July 17, 1951 METHOD OF FORMING TURBINE ROTORS Walter N. Martin and John Y. Riedel, Bethlehem, Pa., assignors to Bethlehem Steel Company, a corporation of Pennsylvania Application December 3, 1945, Serial No. 632,571

Claims.

This invention relates to the method and apparatus for manufacturing turbine rotors for gas turbines, and more especially to the manufacture of rotors for gas turbines for use in a jet propulsion aircraft or the like in which the gases of combustion are led directly into the turbine motor. The turbine rotor drives the compressor which is necessary to furnish heat for combustion. Then the exhaust gas from the turbine,

vfrom which only a small part of the available energy has been extracted is discharged through a tail cone to produce the jet effect which propels the plane.

The gases of combustion discharged into the turbine heat the rotors to a substantially red heat, and it is therefore necessary to obtain high efficiencies to form the rotors of av high alloyed steel to resist oxidation and to withstand the heat to which it is exposed and to carefully forge and treat the rotors to give maximum strength and the highest possible factor of safety.

In carrying the present invention into effect, an ingot containing, for example approximately 16% chromium, 25% nickel, 6% molybdenum and 1.5% manganese, .6% silicon and 51% of iron is rst cast in a mold having a hot top of refractory material forming a sinkhead for maintaining the molten metal which is poured therein fluid at or near the top portion of the ingot for a longer time than that in those portions of the mold which are adjacent to, or subjected to the cooling effect of the metal lower part of the mold. By means of this construction and arrangement the pipes and segregated metalloids due to shrinkage in cooling will be localized within the top portion of the ingot, leaving the body of the said ingot substantially solid and of good quality and to further maintain the top portion of the ingot fluid for a longer period, additional heat is supplied by an electrode which is provided adjacent to the top surface of the ingot for that purpose.

After the ingot has been stripped from the mold and cooled, the part which was cast in the sinkhead is cut olf and the main portion of the ingot machined to form a billet which is then heated to 1950 F. maximum, and subjected to a plurality of hot forging operations between dies in a press to form a blank and between each forging operation the billet is reheated to 1950 F. After the last hot forging operation the blank is heated to 2200 F. and held at that temperature for two and one half hours and then quenched in water. As this type of alloy is not properlyy hardened yby quenching it has tol be 2 hardened by means of a relatively cold forging operation which consists in taking the blank formed by hot forging and heating it to 1200o F. maximum and then subjecting it to a plurality of forging operations between dies in a press and between each forging operation the blank is reheated to 1200 F. It is necessary in the cold forging operation to forge the blank first in the central portion, then at intermediate points and finally adjacent to the peripheral edge at the sides of the blank otherwise the blank will crack or become fractured. After the cold forging operation the blank is again heated to l200 F. and held at that temperature for ten hours for stress relief and then air cooled. The blank is then machined after which the peripheral edge of the rotor is provided with a series of buckets or vanes".

One of the objects of the invention pertains to the method and apparatus for forming a rotor of alloyed steel which consists in taking a cast billet and then subjecting it to a plurality of hot forging operations between dies in a press to compress the same longitudinally and expand it laterally to form a blank and then subjecting the blank to a plurality of relatively cold forging operations to harden the blank.

Another object of the invention relates to the method and apparatus for forming a rotor of alloyed steel adapted to resist oxidation and to withstand heat which consists in taking a cast billet and then subjecting it to a plurality of hot forging operations between dies in a press to compress the same longitudinally and expand it laterally to form a blank free from pipes or segregations, then hardening the blank by subjecting it to a plurality of relatively cold forging operations iirst at the central portion of the blank, then at intermediate points, and finally at the sides adjacent to the peripheral edge of the blank.

A further object of the invention relates to the method and apparatus for forming a rotor of alloyed steel adapted to resist oxidation and withstand heat, which consists in taking a cast billet which has been machined and then subjecting it to a plurality of hot forging operations at 1950 F. to form a blank. Then heating the blank to 2200 F. and hold at that temperature for two and one half hours and then quenching in water, then hardening the blank by a relatively cold forging operation which consists in heating the blank to 1200" F. and then subjecting the blank at this temperature to a plurality of relatively cold forging operations, first at the central portion of the blank, then at intermediate portions and -iinally to the sides of the blank. adjacent to 3 its peripheral edge, and after the cold forging operation again heating the blank to 1200 F. and holding it at that temperature for ten hours for stress relief and thencooling the blank in air.

Other objects of the invention will appear hereinafter.

Havingfthusfgiven ageneral..descriptiorr of the objects of the invention we will now in order to make the saine more clear refer to the accompanying four sheets of drawings forming a part of this specification in which like characters of reference indicate like parts.

Figures 3 to 12, inclusive,-illustratetthewdies and shape of the billets in Ftheestepsiforfthe hot=v forging operation.

Figure 1 is a vertical section ofaningot .mold provided with a hot top of'refractory "material and illustrating the manner of casting ftheingot therein.

Figure 2 is asideelevation ofthe machined billet formed from the ,castingotlvhic'h isho'wn in dotted lines.

. Figure 3 is a sectional view showing thejreciproca'ting forging dies after the rstforging'operation with.. the billet shown in Fig;12 turned over and indicated in dotted lines. Figure 4 is a sectional view of the dies andbillet after. the ,secondV forging operation. In this iigure the billethas been turned over inv relation to.the. positionshown. in Fig. r3, and the lower face ofthe top die is corrugated.

' Figure 5 is a sectional view of the third forging operation in which the saine Idies are used v.and a fiat `plate is inserted between the-'corrugated top die andthe top of the billet to flatten the corrugations .formed therein.

Figure 6 is a sectional view of .the Adies1 and billet after the fourth forging operation.

Figures? and` 8 show the fifthv and sixth'forg- Ving operations in which the `same dies arel used as in Figures 4 and 5.

, Figure 9 .is Va sectional view of the Vdies and billet at the end of theseventh forging operation.

Figure l is a sectional view ofthe diesL and billet Vafter the eighth'step in the forging-oper*- ation in which the lower face of the top die is formed flat.

v Figure 11 is asectional'view of the'dies and billet at the end of the ninth forgingvoperation, and Figure 12 shows a sectional view of the final step in the hot forging operation thereby forining a blah-4. for the relatively cold forging operation.

Figures 13 to 16, inclusive, show-sectionalviews of the vdies and'blanks for the successive-steps in the relatively cold forging operations.

Figure 17 is a plan view of the rotor after'ithe lblank formed by the relatively cold-forging Koperation has been machined, and Figure' 18 is' aside elevation of the rotor shown in Figure 17. Referring/now tothe various characters oflreference in the drawings and first to Figs.:1 to 12, inclusive, the numeral I vindicates a metal mold having the lower portion of: its nroldcavity-tapered inwardly as: at'Z and provided with .a 'bottom plug'. The metal mold isrprovidedwith a refractory hottopshaving a flanget 'for engaging: supporting blocks 6 mounted'on top. ofthe Inetal'rnold I. The refractory hot -topforrnsv a .sinkhead for maintaining themoltenmetal which 7 -ijspoured therein 'fluid at the top kport-ion of the `ingot al longer-time than that inthev lower :portion of themold subjected to thecooling effect ofthe .metal lower. part of :the mold. and tofurtherfmain- .-.tainythetop:. portion: of thegingot l fluidi-.for a:

longer period an electrode 8 is provided adjacent to the top surface of the ingot.

After the ingot has been cast and stripped from the mold and cooled the part which was cast in the sinkhead which might have defects therein is discarded and the main portion of the ingot machined to form a billet 3 of the shape indicated in Figure 2. The billet 9 is then heated to 1950 F. 'The heated billet is then kturned over from the position shown in Figure 2 and placed n in a forging press between dies IIJ and I I in the position indicated in dotted lines in Figure 3 Landfg-iven the rst forging operation thereby shaping the billet I2. The billet I2 is then heat- 151i ed to 1950 Fand turned over from the position .Lrshowniin Figure 3 and placed in a forging press between dies I3 and I4 in the position indicated in dotted lines in Figure 4 and then given a secondforging operation to form the billet I5. In this second forging operation the upper die I3 is adapted to .reciprocate intermittently .and,. .its lower forging surface is corrugated as at It; while the. lower forging die I-*l is adapted to revolve intermittently approximately iny succession and then stop to allow the top corrugated die to engage the top of the lbilletV I5l thereby kneading, compressingA and condensing the metal. The upper die I3 for illustration is vertically movable and may berelatively fixed against rotative movement;- the billet operated upon being rotated-by the lower die I I to change the relation ofthe Successivev operations of the upperd'ie i3 uponthe billet, but the upper die may be rotated with respect to the lower die or the billet maybe'revolved with both dies stationary if desired.

In Figure 5, thesaine dies I3 yand I4 are used as in Figure 4 but a flat plate I'I is insertedbetween the corrugated lower face I6 of theftop die I3 and the top surface ofthe billet I5 to flatten 'the top surface of the saine asV shown at I8. The billetv I5 is again heated to 195G F. and-inserted between dies I I and IS and the billet forged into the shape indicated atf in Figure 6.

It will be noted that in the several figures som'e of the dies have the same shape and where this occurs the same reference numerals will apply thereto and it will be further understoodthat before each ofthe hot forging operations lthe billet is heated to1950 F. The dies used in Figures l .and 8 are the same as those used. in Figures 4 and 5 ,and the billet is treated in. the samernanner with the top die I3 reciprocating and1the .bottom .intermittently rotating 30?. in succession. In Figure 7 the billet 2l isshown with its' top corrugatedpandv in v'Figure 8 the :top of the' billet is flattened asfatI 22. The billet is Vt-heninserted-lbetweefndies IIan'd I-Sanda, billet 23 formed in' the `shapeshown in Figuref) withzfan arcshaped tcpv surface, lthen transferred to'dies I4 and 2li, the latter having a flat lower forging 'surface' adapted to atten the arc shaped topsurface of the billet and forrn itin the shape shown at' 25' in Figure' 10. Billetf is then forgedf-between-dies 11 and 19 to produce a billet `26 shown in Figure 1l andnnally forged between dies'fII and I4 to produce a blank 21 for therelatively c old `forging operation Ias indicated in Figure12. In Figures 11 and l2, gage blocks 28 are, used be'- tween. themes to limit. themovement of the dies to prevent over forging.

These steps complete 4the .hot vforging. Opera tion in Awhich the Cbillet is gradually, .compressed .and .expanded laterally. v Y. 15 -..The zblank 2l. einen heated. no .zzooffEgad held at that temperature for two and one half hours and then given a water quench.

Referring now to Figures 13 to 16, inclusive, which shows the relatively cold forging operation for hardening the blank as this kind of an alloy cannot be hardened properly for the purpose intended by quenching and has to be forged from the central portion of the blank outwardly to prevent cracking or fracturing the blank.

The blank 2l' is rst heated to 1200 F. land inserted between the top and bottom dies 29 and 3U respectively in a press to forge the central portion of the blank 27 into the form shown at 3| in Figure 13. The blank `3l is again heated to 1200 F. and inserted between the same top die '29 and a bottom die 32 which further forges the central and intermediate portions of the blank as indicated at 33 in Figure 14. The blank 33 is reheated to 1200D F. and inserted between `dies 34 and 35 and forged on the side faces of the blank adjacent to the peripheral edges to produce a blank as shown at 36 in Figure 15. The blank is again heated to 1200n F. and inserted between dies 37 and 33 and the extreme peripheral edge of both top and bottom faces of the blank is forged to produce the blank 39 as shown in Figure 16. This completes the relatively cold forging operation for hardening in which the blank is further reduced in thickness and expanded laterally. The blank 39 is then heated to 1200 F. and held at that temperature for ten hours for stress relief and finally air cooled. The blank 39 is then machined to form a rotor 40 or turbine wheel as indicated in Figures 17 and 18.

Although we have shown and described our invention in considerable detail, we do not wish to be limited to the exact and specic details shown and described, but may use such substitutions, modifications or equivalents thereof as are embraced Within the scope of our invention or as pointed out in the claims.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

l. The method of forming a turbine rotor of high alloy steel, containing 16% chromium, 25% nickel, and 6% molybdenum, which consists in hot forging a billet successively at a temperature of 1950 F. in a plurality of sets of dies to form a blank, heating the blank to 2200 F. and holding it at that temperature for two and one half hours, quenching the blank and then reheating the blank to 1200o F. and hardening the blank by subjecting it at that temperature successively in a plurality of sets of dies to a relatively cold forging operation.

2. The method of forming a turbine rotor of high alloy steel, containing 16% chromium, 25% nickel, and 6% molybdenum, which consists in taking a billet and performing successive hot forging operations on the billet after successive heats at approximately 1950 F. to form a blank. heating the blank to 2200" F. and holding it at that temperature for two and one half hours, and then quenching the blank, reheating the blank to 1200 F. and performing successive steps of relatively cold forging operations on the blank from the center of the blank to its peripheral edge to harden the blank, heating the blank again to 1200 F. and holding it at that temperature for ten hours, and then air cooling the blank.

3. The method of forming a turbine rotor of high alloy steel to resist oxidation and withstand heat, and containing 16 chromium, 25% nickel and 6% molybdenum, which consists in taking a billet and performing successive hot forging operations on the billet at a temperature.

of 1950 F. to form a blank, heating the blank l to .2200o F. and holding it at that temperature for two and one half hours, quenching the blank, and then hardening the blank by subjecting it at a temperature of 1200 F. in successive steps to relatively cold forging operations from the center of the blank to its peripheral edge.

4. The method of forming a turbine rotor of an alloy of the class described resistant to corrosion and oxidation at high temperatures, which consists in hot forging a billet in successive operations at a temperature of 1950 F. between dies engaging the ends of the billet to gradually compress the billet and expand it laterally to form a blank, heating the blank to 2200 F. and holding it at that temperature for two and one half hours, quenching the blank, reheating the blank to 1200o F. and hardening the blank by subjecting the faces of the blank to a plurality of relatively cold forging operations at that temperature between dies in steps in succession from the center of the blank to the peripheral edge, holding the blank at a temperature of 1200 F. for ten hours for stress relief, and then cooling the blank in air.

5. 'Ihe method of forming a turbine rotor of an alloy of the class described resistant to corrosion and oxidation at high temperatures, which consists in hot forging a billet in successive operations at a temperature of 1950 F. between dies engaging the ends of the billet to gradually compress the billet and expand it laterally to form a blank, corrugating one end of the bi1- let intermittently at 30 intervals thereby forming successive impressions in the billet, flattening the corrugations after each of the series of the corrugating operations, heating the billet to 2200 F. and holding it at that temperature for two and one half hours, quenching the blank, reheating the blank to 1200 F. and hardening the blank by subjecting the faces of the blank at that temperature to a plurality of cold forging operations between dies in steps in succession from the center of the blank to the peripheral edge, holding the blank at a temperature of 1200 F. for ten hours for stress relief, and then cooling the blank.

WALTER N. MARTIN. JOHN Y. RIEDEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,345,045 Waters June 29, 1920 1,486,365 Cummings Mar. 11, 1924 1,675,264 Fuller June 26, 1928 1,772,876 Parsons et al. Aug. 12, 1930 2,080,368 Ffleld May 11, 1987 2,297,983 Rea Oct. 6, 1942 2,358,799 Franks Sept. 26, 1944 2,393,628 Goldie et al. Jan. 29, 1946 2,398,702 Fleischmann Apr. 16, 1946 2,416,515 Evans. Jr. Feb. 25, 1947 

1. THE METHOD OF FORMING A TURBINE ROTOR OF HIGH ALLOY STEEL, CONTAINING 16% CHROMIUM, 25% NICKEL, AND 6% MOLYBDENUM, WHICH CONSISTS IN HOT FORGING A BILLET SUCCESSIVELY AT A TEMPERATURE OF 1950* F. IN A PLURALITY OF SETS OF DIES TO FORM A BLANK, HEATING THE BLANK TO 2200* F. AND HOLDING IT AT THAT TEMPERATURE FOR TWO AND ONE HALF HOURS, QUENCHING THE BLANK AND THEN REHEATING THE BLANK TO 1200* F. AND HARDENING THE BLANK BY PLURALITY OF SETS OF DIES TO A RELACESSIVELY IN A PLURALITY OF SETS OF DIES TO A RELATIVELY COLD FORGING OPERATION. 